Gln-Gly cleavage: a dominant dissociation site in the fragmentation of protonated peptides

An understanding of the gas-phase dissociation of protonated peptides within the mass spectrometer is essential for automated high-throughput protein identification. In this communication we describe a facile cleavage of the Gln-Gly peptide bond under low-collisional energy conditions. A variety of synthetic peptides have been analysed where key amino acids have been substituted within the sequence PQGPPQQGGR, which is a consensus repeat present in the tryptic peptides of acidic proline-rich protein 1 (PRP-1). The collision-induced dissociation spectra obtained from the PRP-1 tryptic peptides and the synthetic peptides indicate that facile Gln-Gly cleavage occurs when an X-Gln-Gly-Y sequence is present in a peptide, where X is any amino acid and Y any amino acid other than Gly.     

Magnetic and spectral properties of the coligand isomer pair: Cu{N(CN)2}2(pyrazole)2 and Cu{pyrazole · N(CN)2}2

Summary New coligand isomers of composition Cu{N(CN)₂}₂(pz)₂ and Cu{pz · N(CN)₂}₂ (pz = pyrazole) were prepared and studied by measuring their magnetic susceptibilities up to 4.2K and by aid of their e.s.r., ligand field and i.r. spectra. The susceptibility data have been analysed with various models for the exchange-coupled copper(II) polymers. It is shown that the resultant exchange coupling is ferromagnetic for Cu{N(CN)₂}₂(pz)₂ (J 1.1 - 1.4 cm^–1) but antiferromagnetic for Cu{pz · N(CN)₂}₂ (J –0.4 cm^–1). A polymeric chain structure is proposed for Cu{N(CN)₂}₂(pz)₂ havingpseudo-octahedrally coordinated copper(II) and CN-bridging dicyanamide ligands. Its coligand isomer contains anionic chelate ligands, formed by nucleophilic addition between N(CN)₂ and pz in the copper(II) coordination sphere, and giving with this central atom a square-planar system. Definite, but slight axial interaction takes place between these structure units.     

Optimization of molecular geometries in the PCILO and CNDO/2 formalism. The barrier to internal rotation in thioacetaldehyde

The barrier to internal rotation in thioacetaldehyde was investigated within the PCILO and CNDO/2 framework using standard and optimized geometries. The optimized geometries give for the barrier of PCILO a value closer to the experimental one (1.06 kcal mol^?1) whereas the CNDO/2 results yield a qualitatively wrong conformational behavior.     

Synthesen im system {carbonylmetallat/ketenimin/säure}: XXX. Neue ferra- und rhenaazetidine

The metal carbonyl anions [Fe(η-C₅H₅(CO)₂]^? and [Re(CO)₅] undergo regio- and site-specific [2 + 2]-cycloadditions with the ketenimines Ph₂CCNR (R = Me, Ph) to give the (isolable) anionic complexes [L_n$\text{M{C(CPh}{}_2\text{)N(R)C}$(O)}]^? (L_nM = Fe(η-C₅H₅)CO, Re(CO)₄) which have been alkylated and acylated at the exocyclic oxygen atom of the carbonyl function. The result is stable neutral complexes having a metallaazetidine structure which is composed of an α-metallated enamine and an N,O carbene part. IR, ¹H, and ¹³C NMR data are presented.     

Optisch-aktive α-Phenyläthyl-thiuroniumsalze als neue Spaltbasen. Darstellung der beiden Antipoden der 3,3-Diphenyl-3-cyano-1-methyl-propancarbonsäure-(1)

Zusammenfassung Es wird die Herstellung neuer, optisch aktiver -Phenyläthyl-thiuroniumsalze durch Spaltung des racemischen -Phenyläthyl-thiuroniumacetates mit d-Camphersäure beschrieben. Die Eignung der opt.-aktiven Thiuroniumsalze zur Spaltung von racemischen Carbonsäuren wird an 2 Beispielen gezeigt.Für die Anregung zu dieser Untersuchung und manche Diskussion während derselben danke ich Herrn Prof. Dr.H. Bretschneider.     

Retention in coupled capillary column supercritical fluid chromatography with lipids as model compounds

Summary We have investigated to which extent retention data, acquired on single capillary columns, can be used for predicting retention factors in a coupled column system. For this purpose we utilized a model mixture of 18 lipid components with widely different vapor pressures and polarities. The sample was chromatographed on two columns, SB-biphenyl-30 (70% methyl-30% biphenylpolysiloxane) and SB-cyanopropyl-50 (50% methyl-50% cyanopropylsiloxane). Experimental retention factors, acquired in coupled column systems with two columns connected in different order, were thus compared with values calculated from runs on each single column. The agreement between calculated and experimental values generally was better than 5% without any pressure drop correction.To study the possibility of predicting retention behavior in a wide pressure range from a limited number of experiments, we also investigated the relation between solute retention and mobile phase density. We found that all data could be fitted to second order equations, which gives the possibility to optimize the resolution with respect to pressure from a limited number of runs at different pressures.     

Trennung,Identifizierung und Bestimmung von Bactericiden auf der Basis von halogenierten Aromaten mittels Gas-Chromatographie

The separation of a mixture of 22 bactericides has been achieved by gas chromatography on columns with silicone rubber W-982 as stationary phase with temperatures between 100° and 300°C. The unchanged compounds as well as their silylation products have been used. The latter are more conveniently used especially for the quantitative determination. To be able to calculate the retention indices after Kovats gas chromatography has been performed isothermally at 180°C for the more volatile compounds and at 250°C for all other bactericides.The retention indices obtained under these conditions are tabulated together with the limits of detection.     

Electron correlation as the driving force for charge transfer: charge migration following ionization in N-methyl acetamide

A hole charge created in a molecule, for instance, by ionization, can migrate through the system solely driven by electron correlation. The migration of a hole charge following ionization in N-methyl acetamide (a molecular system containing a peptide bond) is investigated. The initial hole charge is localized at one specific site of the molecule. Ab initio calculations show that nearly 90% of the hole migrates to a remote site of the molecule in 4.2 fs. This migration of charge is highly efficient and ultrafast. The underlying mechanism for this migration of a hole charge is identified and compared with a simple model.     

Isolation of selenium organic species from antarctic krill after enzymatic hydrolysis

Total selenium content and its distribution in the soluble and insoluble protein-bound fractions obtained after aqueous extraction of antarctic krill samples were determined. About 26% of the total selenium (2.4 g g^–1 dry weight) was found in the supernatant; the rest was in the pellet. Isolation of low molecular selenium-containing fractions was also performed by enzymatic digestion of the protein, followed by size-exclusion chromatography in conjunction with atomic absorption spectrometry. From the applied various proteinases (pronase E, subtilisin Carlsberg, trypsin, chymotrypsin, proteinase and proteinase N from Bacillus subtilis and Novo 0.6 MPX enzyme), the treatment with pronase E led to best recovery of selenium. About 96% of the total Se was found in the hydrolysate, mainly in low molecular weight fractions. Eighty percent of the Se species were in fractions with molecular weights in the range of amino acids and short peptides. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS) allowed the identification of selenomethionine and the assumption that selenocystine or its derivatives were the main species in these fractions.     

Pressurised hot water extraction-microporous membrane liquid-liquid extraction coupled on-line with gas chromatography-mass spectrometry in the analysis of pesticides in grapes

Pressurised hot water extraction-microporous membrane liquid-liquid extraction was coupled on-line with gas chromatography-mass spectrometry (PHWE-MMLLE-GC-MS) for the analysis of pesticides in grapes. MMLLE serves as a trapping step after PHWE. Water from PHWE is directed to the donor side of the membrane unit and the analytes are extracted to the acceptor solution on the other side. The role of MMLLE is to clean and concentrate the extract before on-line transfer to the GC via a sample loop and an on-column interface using partially concurrent solvent evaporation. The extraction conditions were investigated, and then the quantitative features such as linearity, limit of quantification (LOQ), extraction yield and enrichment factors. LOQs in the range 0.3-1.8 microg kg(-1) were achieved. Procymidone and tetradifon were found in the skins of the grapes. The results were in good agreement with those obtained by liquid-solid and ultrasonic extractions.